Insulinoma in Dogs - Causes, Symptoms and Treatment

To understand what insulinomas in dogs are, we need to explain the structure and function of the pancreas, i.e. the organ which is affected by this type of canine tumor. The pancreas is known as a mixed heterocrine gland as it has both endocrine and exocrine functions:

• Exocrine pancreas: is related to the digestive system. It secretes pancreatic juice, necessary for the digestion of food.
  
  
• The endocrine pancreas: contains pancreatic islets (also known as islets of Langerhans) which are made up of alpha cells (glucagon-secreting), beta cells (insulin-secreting) and delta cells (somatostatin-secreting). These cells produce some of the most important hormones in the canine body, specifically those which regulate blood glucose levels.

Now we know more about the structure and function of the pancreas, we explain how the tumors affect it. As an insulinoma affects the pancreatic beta cells, it will have a bearing on insulin production. Insulin is a hormone which is released in response to glucose in the blood, allowing the glucose to enter cells and be used as energy. When a dog has an insulinoma, these cells begin to permanently secrete excessive amount of insulin, resulting in hypoglycemia, i.e. low blood-glucose levels in dogs.

Within the insulinoma, we can find benign (adenoma) and malignant (carcinoma) cell proliferations. Pancreatic carcinomas have a high mortality rate and often metastasize to the mesentery, liver, spleen, and regional lymph nodes. Fortunately, development of insulinoma tumors are rare in the dogs.

Canine insulinoma usually appears in dogs aged between 3 and 14 years of age, although they are more frequent in older ages (9+ years of age). There is no sexual predisposition, but there is a predisposition according to breed. There appears to be a higher incidence in the German Shepherd, Golden Retriever, Poodle, Irish Setter, Fox Terrier and Boxer dog breeds.

The clinical signs associated with canine insulinoma occur as a result of sustained hypoglycemia and stimulation of the sympathoadrenal system. Specifically, insulinoma in dogs usually presents with:

• Weakness and lethargy (due to glucose deficit of the central nervous system)
• Abnormal behaviors (e.g. nervousness, irritability, etc.)
• Weakness in the posterior third, cramps and muscle fasciculations (twitching)
• Collapse
• Ataxia (incoordination)
• Seizures

Other less frequent clinical signs that can be detected in canine patients with insulinoma include:

• Polyuria (increased urination)
• Polydipsia (excessive drinking)
• Polyphagia (increased hunger)
• Anorexia
• Weight gain
• Diarrhea
• Syncope (fainting)
• Head tilt
• Urinary incontinence
• Blindness

Take a look at two of these canine insulinoma symptoms in more depth with our articles on syncope in dogs and why a dog is losing a lot of weight.

The exact etiology of insulinoma in dogs is unknown. As with all neoplasms, insulinoma is caused by a genetic alteration that gives rise to disorganized cell proliferation. However, the specific cause that triggers this genetic alteration is not yet known to veterinary science. There is a genetic predisposition, as seen in the list of dog breeds with a propensity for developing insulinoma.

The diagnosis of canine insulinoma should be based on the following factors:

• Clinical history and physical examination: as we have already pointed out, dogs with this pathology present clinical signs fundamentally associated with sustained hypoglycemia.
  
  
• Blood analysis (complete blood count and biochemistry): the most indicative parameter of canine insulinoma is the detection of a state of fasting blood sugar (values less than 60 mg/dl), which is due to the excessive production of insulin by tumor cells. However, to confirm hypoglycemia, an isolated determination is not enough. It is necessary to chart measurements every hour, during an 8-hour fasting period.
  
  
• Histopathological analysis: it is performed once the tumor has been removed and allows the diagnosis to be confirmed. Microscopically, pancreatic cell neoplasms are made up of well-differentiated cells with few mitoses, but great facility for metastasizing.

Learn more about diagnosing disease in canines with our guide to understanding a dog's blood test.

If your dog is diagnosed with an insulinoma, it is understandable you will want to know if it is curable. In some cases, surgical intervention can remove it completely and leave the dog with a functioning pancreas. In other cases, metastasis and organ failure mean the prognosis will be poor. There are two types of treatment for insulinoma in dogs.

Surgical treatment of canine insulinoma

The objective of surgery is to remove the pancreatic tumor, either partially or in totality. The latter is always preferred. If the tumor has metastasized to tissues such as the mesentery, liver or lymph nodes, these cancerous tissues need to be removed also.

Surgical treatment is recommended. Even if it is only possible to perform a partial removal, the symptoms will subside for a variable period of time, ranging from months to a year. It can also help the success of medical therapy. However, surgery is discouraged in critically ill patients due to risks of general anesthesia.

Although surgery is the treatment of choice in all stable dogs, it must be taken into account that a series of postoperative complications may occur:

• Pancreatitis: due to handling of the pancreas during surgery. To prevent its appearance, gentle management of the pancreas must be performed during surgery, adequate fluid therapy is required before, during and after the operation, and adequate postoperative nutrition must be provided.
  
  
• Diabetes mellitus: when the tumor is removed, the pancreas may not be able to synthesize enough insulin as the rest of the beta cells are atrophied. In these cases, exogenous insulin should be administered until the pancreas regains its functional ability to produce insulin.
  
  
• Sustained hypoglycemia: occurs when there are metastases that continue to produce insulin. In these cases, additional medical treatment is required.

Medical treatment

Medical treatment will be necessary both in dogs where surgery is not possible, as well as those which undergoes surgical removal of some or all of the tumor. The medical treatment of insulinoma in dogs is usually one of two options:

• Treatment of acute hypoglycemic shock: it is an emergency situation in which the animals suffer a convulsive shock or seizure. In these cases, guardians must be forewarned and act quickly by rubbing a sugary solution (such as jam or honey) into the oral cavity. The oral mucosa has the ability to quickly absorb the glucose contained in these foods, thus resolving the convulsive shock in about 30-120 seconds.
  
  
• Treatment of chronic or sustained hypoglycemia: the objective of this part of the treatment is to palliate the symptoms derived from hypoglycemia and prevent the appearance of acute crises. Chemotherapy protocols for dogs should not be used, since they all cause serious side effects. Medical treatment should only be aimed at increasing glucose absorption in the intestine and decreasing insulin secretion. Specifically, a dietary treatment should be carried out with more frequent meals and avoiding periods of prolonged fasting. A combination of dry and wet food is recommended, along with very light exercise. Pharmacological treatment should be added to dietary treatment, usually in the form of glucocorticoids or diazoxide.

Unfortunately, the prognosis for canine insulinoma ranges from guarded to poor. This is because most of these tumors when detected in dogs are malignant.

The life expectancy of dogs with insulinoma depends on the treatment that is established:

• In dogs receiving only medical treatment: life expectancy is 12 months.
• In dogs that undergo surgical treatment: one third die from intra- or postoperative complications, another third live less than 6 months and the remaining third may have a life expectancy of 12 to 14 months.

Whether or not surgery is an option for your dog will depend on the severity and size of the tumor. In some cases, the prohibitive cost along with the poor prognosis will mean palliative care for the dog is the chosen course of action.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

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